Will native trees thrive in the future?

LOOK around you. The Cornish landscape, particularly the Area of Outstanding Natural Beauty that we know and love, is composed of many things – ancient rocks, high moors and deep valleys, rolling fields, Cornish hedges, buildings, roads and, perhaps above all, trees.

Trees? Surely we are always thought of, and described, as a 'treeless' county. True, we don't have the dense woodlands of the south-east Weald or the remains of the great forests of the Midlands. But there are far more trees in our Cornish landscape than you might think – from the stunted hawthorns near the coast, to the wild oaks along the river valleys.

We also see a large number of 'non-native' trees. Some were brought over to populate the great gardens such as Trebah and Trelissick in the 19th century and apart from the pesky rhododendron, most are an asset to the landscape. But today some are being planted by landowners and our councils that are the wrong trees in the wrong place.

A lack of understanding of which trees are native to Cornwall has led to inappropriate planting of 'foreign' woodland and hedgerow species. Examples are field maple, exotic alders, pines and English oak.

What is Cornish woodland? Which are Cornwall's native trees?

Let's go back to just after the last ice age. Cornwall Council's historic environment service explains: "Climate and vegetation changed rapidly after 8000BC. From cold grassland and patches of birch woodland, the fuller wildwood of oak and hazel with some elm had developed by 6000BC. Sometime after 5500BC Britain became separated from the continent by the rising sea." So 'native' trees are those which were here after we separated from Ireland but before the land bridge to Europe was submerged and Britain became an island.

Analysis

Careful analysis of ancient tree pollen preserved in successive layers in the wet Cornish marshes proves that our native woodlands, following the last ice age, were composed almost entirely of sessile oak and hazel which were found on dry land and throughout the upland forested areas and alder, which was found in damp valley bottoms. These then are the true native woodland trees of Cornwall. To this we can add the Cornish elms which genetically can be traced to Brittany and were mostly brought over in the Bronze Age for shelter belts around fields; they are very resistant to salt winds and spread by suckering not by seed. The shorter and much narrower Cornish elm is distinct from the English elm which is only found east of the Tamar, and today mostly only in Sussex.

Many Cornish landscapes now of bare, treeless Cornish hedges were, for thousands of years, densely vegetated with shelter-giving veils of elm trees. Yet Dutch elm disease caused as much devastation to the Cornish elms as to their English relation. Original elms can still be seen in parts of the Scillies where elm disease has not caused such destruction. Elms do still occur in Cornwall – often where the roots have survived and sent up new shoots after the disease killed only the above-ground tree.

Cornwall's native oak trees may look at first glance like English oaks – but they are in fact a totally different species that occurs along the Atlantic Coastal (Celtic) fringe of Europe. The main differences are that Cornish (sessile) oaks have a stalk on the leaf and no stalk on the acorn, whereas English oaks have no stalk on the leaf and a long stalk on the acorn. Look closely and check for yourself.

So where best then to see our truly native trees? All along the Helford and the Fal and in parts of Tehidy Woods are good places. Further afield, Dizzard Woods, clothing the north coast cliffs, are among the oldest sessile oak woods in Cornwall.

The widespread sycamore is a relatively late arrival having been brought over from Europe in the 1600s. Its wind-dispersed seeds freely colonise all the places from which we have removed our native trees. However it is possible sycamore could become the replacement for elm in our hedgerows as it spreads vigorously and is resistant to salt winds.

As 'development' pressure grows and climate change increases, it will be interesting to see how our landscape changes and how trees, and our native species in particular, fare in the years that lie ahead and whether our native sessile oak woodlands will continue to thrive.